Gerotor-type oil pump

ABSTRACT

An oil pump includes a housing defining a pump cavity having an inner circumferential wall with a first segment located in a low-pressure side of the pump cavity. The first segment defines a recessed cutout. A gerotor pump set is disposed in the cavity and includes an inner drive rotor and an outer driven annulus. An outer circumferential wall of the outer annulus and the cutout cooperate to form an increased radial clearance to reduce friction losses between the outer annulus and the housing.

TECHNICAL FIELD

The present disclosure relates to oil pumps and more specifically to gerotor-type oil pumps.

BACKGROUND

A typical vehicle may include one or more oil pumps for circulating oil through the engine and/or the automatic transmission. Typically, the engine includes a dedicated oil pump and the transmission includes a dedicated oil pump. The oil pumps may be mechanically driven by a crankshaft of the engine. More recently, electric oil pumps have been introduced to operate the transmission when the engine is OFF.

A gerotor-type oil pump may be used for the engine or the transmission. This type of oil pump is a positive-displacement pump that includes a pair of internal and external gears disposed within a pump chamber. The internal gear is eccentrically mounted within the external gear. The internal gear is rotationally coupled to a driveshaft powered mechanically or electrically. Rotation of the inner gear causes the outer gear to rotate in the same direction. As the inner and outer gears rotate, chambers defined between lobes of the gears increase and decrease in size forcing oil through the pump.

SUMMARY

According to one embodiment, an oil pump includes a housing defining a pump cavity having an inner circumferential wall with a first segment located in a low-pressure side of the pump cavity. The first segment defines a recessed cutout. A gerotor pump set is disposed in the cavity and includes an inner drive rotor and an outer driven annulus. An outer circumferential wall of the outer annulus and the cutout cooperate to form an increased radial clearance to reduce friction losses between the outer annulus and the housing.

According to another embodiment, an oil pump includes a housing defining a face and an inner circumferential wall cooperating with the face to define a pump cavity having a high-pressure side and a low-pressure side. The circumferential wall defines a recessed cutout extending arcuately along a portion of the circumferential wall in the low-pressure side. A gerotor pump set is disposed in the cavity and includes an outer driven annulus defining internal lobes and an outer circumferential wall circumscribed by the inner circumferential wall. The gerotor pump set further includes an inner drive rotor eccentrically received within the outer annulus and defining external lobes cooperating with the internal lobes to define a plurality of fluid chambers. A driveshaft extends through the face and is coupled to the inner drive rotor. The driveshaft is configured to rotate the gerotor pump set within the cavity such that the outer annulus rotates relative to the inner circumferential wall. The cutout forms an increased radial clearance between the inner and outer circumferential walls to reduce friction losses when the outer annulus rotates relative to the housing.

According to yet another embodiment, an oil pump includes a housing defining a pump cavity and a gerotor pump set disposed in the cavity. The gerotor pump set has an inner drive rotor and an outer driven annulus. A pump cover has a front face disposed over the pump cavity. The front face defines an inlet port and an outlet port. A portion of the outlet port is radially inboard of a root circle of the inner drive rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross-sectional view of a gerotor-type oil pump.

FIG. 2 is a front view of the oil pump with the cover removed for illustrative purposes.

FIG. 3 is a perspective view of the cover of the oil pump.

FIG. 4 is a perspective view of the pump housing of the oil pump.

FIG. 5 is front view of the oil pump with the gerotor pump set shown in hidden lines for illustrative purposes.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the embodiments. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.

Referring to FIGS. 1 and 2, an oil pump 20 includes a housing 22. The pump housing 22 defines a cylindrical pump cavity 26 having a back face 28 and an inner circumferential wall 30 extending axially from the back face 28. A gerotor pump set 32 is disposed within the pump cavity 26 and is configured to circulate oil. The set 32 includes an inner drive rotor 34 and an outer driven annulus 36. The rotor 34 is eccentrically supported within the annulus 36 and defines external lobes 38 cooperating with internal lobes 40 of the annulus 36 to define a plurality of fluid chambers 42. The volume of the fluid chambers 42 varies depending upon the amount of meshing between the lobes 38, 40. This variation in volumes creates pumping action as will explain in more detail below.

A cover 44 is attached to the housing 22 to seal the pump cavity 26. The cover 44 may be attached to the housing 22 with fasteners or the like. The cover 44 may include a front face 46 disposed over the pump cavity 26 and the gerotor pump set 32. In the illustrated embodiment, the inlet and outlet ports 48 and 50 are defined in the cover 44. The inlet and outlet ports 48, 50 extend through the front face 46 to be in fluid communication with the pump cavity 26. The cover 44 may include connection features for attaching external fluid conduits to the inlet and outlet ports 48, 50.

The oil pump 20 may be driven mechanically, such as by an engine, or electrically, such as by an electric motor. The illustrated oil pump 20 is an electric pump powered by an electric actuator, e.g., motor 60, disposed within a motor cavity 62 of the housing 22. A driveshaft 64 of the motor 60 extends axially through the back face 28 and into the pump cavity 26. The rotor 34 is rotationally fixed to the driveshaft 64 such as by a spline connection. The pump 20 is operated by rotating the rotor 34, such as in the counterclockwise direction shown in FIG. 2. The spinning rotor 34 drives the annulus 36 in the same direction as the rotor 34 due to meshing of the lobes 38 and 40. As the rotor 34 and the annulus 36 rotate relative to each other in the pump cavity 26, oil is drawn into the chambers 42 as the chamber size increases and is expelled through the outlet port 50 as the chamber size decreases.

Referring to FIGS. 3 and 4, the cover 44 defines kidney-shaped inlet and outlet ports 48, 50, and the back face 28 defines recessed kidney-shaped inlet and outlet shadow ports 66 and 68. The profiles of the shadow ports 66 and 68 on the back face 28 typically mirror the profiles of the inlet and outlet ports 48 and 50. The kidneys serve as a portion of the inlet and outlet ports and provide fluid paths from the inlet to the pump cavity and from the pump cavity to discharge.

Referring back to FIG. 2, an oil film is formed between the inner circumferential wall 30 of the pump body 26 and an outer circumferential wall 70 of the annulus 36. The oil film creates a fluid bearing for the annulus 36 during operation of the pump 20. This oil film, however, also creates friction losses due to the effect of the fluid's viscosity acting on the rotating annulus 36. The magnitude of the friction loss is a function of the clearance (radially distance) between the inner and outer circumferential walls 30, 70. Increasing the clearance reduces the magnitude of the friction loss. While increasing the clearance may reduce friction loss, excessive clearance results in unsatisfactory pump performance. The inner and outer circumferential walls 30, 70 may be concentric, and the outer circumferential wall 30 is responsible for maintaining the concentricity of the annulus 36. Excessive clearance between the circumferential walls 30, 70 may result in excessive wobble of the annulus 36. As such, a typical clearance range is between 0.020 and 0.200 millimeters (mm).

The pump cavity 26 can generally be divided into a high-pressure side 72 and a low-pressure side 74. The dividing line 75 extends through the center of the annulus 36 and through the center of the rotor 34. The low-pressure side 74 includes the inlet port 48 and the inlet shadow port 66, and the high-pressure side 72 includes the outlet port 50 and the outlet shadow port 68.

During operation of the pump 20, the annulus 36 is driven towards the segment 76 of the inner circumferential wall 30 located on the high-pressure side 72 and is driven away from the segment 78 of the inner circumferential wall 30 located on the low-pressure side 74. The segment 76 acts as a thrust surface that supports the annulus 36 in place whereas the segment 78 is typically unloaded. Since the segment 78 is not acting as a thrust surface, the clearance between the segment 78 and the annulus 36 can be increased to reduce friction loss of the pump 20 without losing concentricity of the annulus 36.

Referring to FIGS. 2 and 4, one or more cutouts 80 are recessed into the segment 78 to increase the clearance between the inner circumferential wall 30 and the outer circumferential wall 70. The cutout(s) 80 may be recessed between 0.2 and 2.0 mm. In the illustrated embodiment, a pair of cutouts 82 and 84 are defined into the segment 78. The cutouts 82 and 84 may be circumferentially spaced apart from each other to form a bumper 87 on the low-pressure side 74. The bumper 87 provides a safeguard to prevent the annulus 36 from losing concentricity due to a disturbance in the system. The bumper 87 is an optional feature.

The inner circumferential wall 30 defines an inner surface 86. The cutout 82 may have a first surface 88 extending radially outboard from the inner surface 86 and a back surface 90 extending circumferentially from the first surface 88 to a second surface 92. The second surface 92 may extend radially inboard from the back surface 90 to the inner surface 86. The cutout 82 may only extend axially along a portion of the inner circumferential wall 30. In the illustrated embodiment, the cutout 82 extends partially down the wall 30 from an end 94 of the pump housing 22 towards the back face 28. This creates a ledge 96 that is continuous with the inner surface 86. The ledge 96 provides support to ensure the concentricity of the annulus 36 is maintained in the event of disturbances. In other embodiments, the cutout may extend to the back face 28. The cutout 84 may have a same or similar structure as the cutout 82, and for brevity, will not be described again. In the illustrated embodiment, the cutouts 82 and 84 have a same arc length, height, and depth, but in other embodiments the cutouts 82 and 84 may a have different arc length, height, and/or depth.

During operation of the pump 20, an oil film is also formed between the gerotor set 32 and the front and back faces 46, 28 of the pump cavity 26. These oil films also create friction losses due to the effect of the fluid's viscosity acting on the rotating rotor 34 and annulus 36. Removing material from the front and back faces 46, 28 reduces the friction losses similar to the cutouts 80. The faces already have material removed for the inlet and outlet ports 48 and 50 and the inlet and outlet shadow ports 66, 68, but by enlarging these ports or creating additional ports friction losses can be further reduced.

Referring to FIGS. 4 and 5, the inlet shadow port 66 may include a main portion 100 and a friction-reducing portion 102. The main portion 100 is similar to a traditional shadow port whereas the friction reducing portion 102 is an additional cutout defined in the back face 28 for the purposes of reducing fluid friction between the rotor 34 and the back face 28. The main portion 100 includes an inner arcuate edge 104 having a common center with the rotor 34 and an outer arcuate edge 106 having a common center with the annulus 36. The arcuate edge 104 has a radius that substantially matches the root radius of the rotor 34. A root radius is a radius of the root circle 105 of the rotor 34. A root circle is a circle that coincides with the bottoms 107 of the lobes 38. Thus, the main portion 100 is disposed radially outboard of the root circle 105 of the rotor 34.

The friction-reducing portion 102 is disposed within the root circle 105 of the rotor 34 to reduce friction between the back face 28 and the rotor 34. The friction-reducing portion 102 includes an inner arcuate edge 108 having a common center with the rotor 34. The arcuate edge 104 defines the outer arcuate edge of the friction-reducing portion 102. The friction-reducing portion 102 may include a vent 110 extending radially inward towards the driveshaft 64.

The recess depth of the main portion 100 may be deeper than the friction-reducing portion 102. For example, the main portion 100 may have a depth between 1.0 and 10.0 mm, and the friction-reducing portion 102 may have a depth between 0.25 and 2.0 mm. In other embodiments, the depth of the portions 100 and 102 may be the same. That is, the shadow port 66 may be a single, enlarged port that has a portion disposed within the root circle 105 of the rotor 34.

The outlet shadow port 68 may include a main portion 120 and a friction-reducing portion 122. The main portion 120 may similar to a traditional outlet shadow port whereas the friction reducing portion 122 is an additional cutout defined in the back face 28 for the purposes of reducing friction between the rotor 34 and the back face 28. The main portion 120 includes an inner arcuate edge 124 having a common center with the rotor 34 and an outer arcuate edge 126 having a common center with the annulus 38. The arcuate edge 124 has a radius that substantially matches the root radius of the rotor 34. Thus, the main portion 120 is disposed radially outboard of the root circle 105 of the rotor 34.

The friction-reducing portion 122 is disposed within the root circle 105 of the rotor 34 to reduce friction between the back face 28 and the rotor 34. The friction-reducing portion 122 includes an inner arcuate edge 128 having a common center with the rotor 34. The arcuate edge 124 defines the outer arcuate edge of the friction-reducing portion 122. Like the inlet shadow port 66, the recess depth of the main portion 120 may be deeper than the friction-reducing portion 122 or the same depth.

In the illustrated embodiment, both the inlet shadow port 66 and the outlet shadow port 68 include a friction-reducing portion. In other embodiments, only one of the inlet and outlet shadow ports may include a friction reducing portion. In yet another embodiment, neither of the inlet and outlet shadow ports may include a friction reducing portion.

Referring to FIG. 3, the inlet port 48 may include a main portion 130 and a friction-reducing portion 132. The main portion 130 is similar to a traditional inlet port whereas the friction reducing portion 132 is an additional cutout defined in the front face 46 for the purposes of reducing friction between the rotor 34 and the front face 46. The main portion 130 includes an inner arcuate edge 134 having a common center with the rotor 34 and an outer arcuate edge 136 having a common center with the annulus 38. The arcuate edge 134 has a radius that substantially matches the root radius of the rotor 34. Thus, the main portion 130 is disposed radially outboard of the root circle 105 of the rotor 34.

The friction-reducing portion 132 is disposed within the root circle 105 of the rotor 34. The friction-reducing portion 132 includes an inner arcuate edge 138 having a common center with the rotor 34. The arcuate edge 134 defines the outer arcuate edge of the friction-reducing portion 132. The friction-reducing portion 132 may include a vent 140.

The outlet port 50 may include a main portion 150 and a friction-reducing portion 152. The main portion 150 may be similar to a traditional outlet port whereas the friction reducing portion 152 is an additional cutout defined in the front face 46 for the purposes of reducing friction between the rotor 34 and the front face 46. The main portion 150 includes an inner arcuate edge 154 having a common center with the rotor 34 and an outer arcuate edge 156 having a common center with the annulus 38. The arcuate edge 154 has a radius that substantially matches the root radius of the rotor 34. Thus, the main portion 150 is disposed radially outboard of the root circle 105 of the rotor 34.

The friction-reducing portion 152 is disposed within the root circle 105 of the rotor 34. The friction-reducing portion 152 includes an inner arcuate edge 158 having a common center with the rotor 34. The arcuate edge 154 defines the outer arcuate edge of the friction-reducing portion 152. In the illustrated embodiment, both the inlet port 48 and the outlet port 50 include a friction-reducing portion. In other embodiments, only one of the inlet and outlet ports 48, 50 includes a friction reducing portion. In yet another embodiment, neither of the inlet and outlet ports include a friction reducing portion.

The main portions 130 and 150 are deeper than the friction reducing portions 132, 152, and extend down through the cover 44 to the inlet and outlet connection ports. The main portions have axially extending walls 160, 162 and the shallow portions have bottom walls 164, 166 extending radially from the axially extending walls 160, 162.

The friction-reducing cutouts, e.g. cutout 80, and the friction reducing portions, e.g. friction reducing portion 102, may both be included in the pump 20 (as is shown in the illustrated embodiment) or only one of these features may be present. For example, an oil pump may include both the circumferential wall cutouts and the friction reducing portions, or an oil pump may only include the circumferential wall cutouts, or an oil pump may only include the friction reducing portions. Additionally, each of the ports need not include the friction-reducing portions. For example, the oil pump may only include friction reducing portions on the outlet port 50 and the outlet shadow port 68, or the oil pump may only include friction-reducing portions on the inlet port 48 and the inlet shadow port 66.

While the oil pump 20 is shown as an electronic pump for a transmission, the friction-reducing techniques described herein are broadly applicable to any gerotor-type oil pump. That is, the oil pump 20 is not limited to any particular application or power source. For example, the above teachings may be applied to a gerotor-type engine oil pump or to a mechanically powered gerotor-type oil pump for a transmission. This disclosure is also not limited to the automotive field and can be used in gerotor-type oil pumps for other fields.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, to the extent any embodiments are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, these embodiments are not outside the scope of the disclosure and can be desirable for particular applications.

The following is a list of reference numbers shown in the Figures. However, it should be understood that the use of these terms is for illustrative purposes only with respect to one embodiment. And, use of reference numbers correlating a certain term that is both illustrated in the Figures and present in the claims is not intended to limit the claims to only cover the illustrated embodiment.

PARTS LIST

-   -   20 oil pump     -   22 housing     -   26 pump cavity     -   28 back face     -   30 wall     -   32 pump set     -   34 drive rotor     -   36 annulus     -   38 external lobes     -   40 internal lobes     -   42 fluid chambers     -   44 cover     -   46 front face     -   48, 50 outlet ports     -   60 motor     -   62 motor cavity     -   64 driveshaft     -   66, 68 shadow ports     -   70 wall     -   72 high-pressure side     -   74 low-pressure side     -   75 dividing line     -   76, 78 segment     -   80, 82, 84 cutouts     -   86 inner surface     -   87 bumper     -   88 first surface     -   90 back surface     -   92 second surface     -   94 end     -   96 ledge     -   100, 120, 130, 150 main portion     -   102, 122, 132, 152 friction-reducing portion     -   104, 108, 124, 134, 138, 154, 158 inner arcuate edge     -   105 root circle     -   106, 126, 136, 156 outer arcuate edge     -   107 bottoms     -   110, 140 vent     -   160, 162 axially extending walls     -   164, 166 bottom walls 

What is claimed is:
 1. An oil pump comprising: a housing defining a pump cavity having an inner circumferential wall with a first segment located in a low-pressure side of the pump cavity, the first segment defining a recessed cutout; and a gerotor pump set disposed in the cavity and including an inner drive rotor and an outer driven annulus, wherein an outer circumferential wall of the outer annulus and the cutout cooperate to form an increased radial clearance to reduce friction losses between the outer annulus and the housing.
 2. The oil pump of claim 1, wherein the first segment further defines a second recessed cutout circumferentially spaced from the cutout.
 3. The oil pump of claim 2, wherein the first segment defines a bumper between the cutout and the second cutout.
 4. The oil pump of claim 1, wherein the recessed cutout has a depth of at least 0.2 millimeters.
 5. The oil pump of claim 1, wherein the inner circumferential wall defines an inner surface, and recessed cutout has a first surface extending radially outboard from the inner surface, a back surface extending circumferentially from the first surface, and a second surface extending radially inboard from the back surface to the inner surface.
 6. The oil pump of claim 1, wherein the pump cavity further has a face defining a recessed outlet shadow port having a first portion radially inboard of a root circle of the inner drive rotor.
 7. The oil pump of claim 6, wherein the outlet shadow port further has a second portion radially outboard of the root circle.
 8. The oil pump of claim 7, wherein the first portion is recessed shallower than the second portion.
 9. The oil pump of claim 1 further comprising a cover attached to the housing to seal the pump cavity, the cover defining a recessed port located radially inboard of a root circle of the inner drive rotor.
 10. An oil pump comprising: a housing defining a face and an inner circumferential wall cooperating with the face to define a pump cavity having a high-pressure side and a low-pressure side, wherein the circumferential wall defines a recessed cutout extending arcuately along a portion of the circumferential wall in the low-pressure side; a gerotor pump set disposed in the cavity and including: an outer driven annulus defining internal lobes and an outer circumferential wall circumscribed by the inner circumferential wall, and an inner drive rotor eccentrically received within the outer annulus and defining external lobes cooperating with the internal lobes to define a plurality of fluid chambers; and a driveshaft extending through the face and coupled to the inner drive rotor, the driveshaft being configured to rotate the gerotor pump set within the cavity such that the outer annulus rotates relative to the inner circumferential wall, wherein the cutout forms an increased radial clearance between the inner and outer circumferential walls to reduce friction losses when the outer annulus rotates relative to the housing.
 11. The oil pump of claim 10, wherein the circumferential wall further defines a second recessed cutout extending arcuately along another portion of the circumferential wall that is circumferentially spaced from the cutout and is in the low-pressure side.
 12. The oil pump of claim 11, wherein the circumferential wall between the cutout and the second cutout forms a bumper.
 13. The oil pump of claim 10 further comprising a cover defining an inlet port and an outlet port, wherein a portion of the inlet port or the outlet port is disposed radially inboard of a root circle of the inner drive rotor.
 14. The oil pump of claim 10 further comprising a cover defining an outlet port, wherein a portion of the outlet port is disposed radially inboard of a root circle of the inner drive rotor.
 15. The oil pump of claim 10 further comprising a cover having a face disposed over the pump cavity and defining a recessed portion at least partially disposed radially inboard of a root circle of the inner drive rotor.
 16. The oil pump of claim 10 further comprising an electric machine operably coupled to the driveshaft.
 17. An oil pump comprising: a housing defining a pump cavity; a gerotor pump set disposed in the cavity and including an inner drive rotor and an outer driven annulus; and a cover including a front face disposed over the pump cavity, the front face defining an inlet port and an outlet port, wherein a portion of the outlet port is radially inboard of a root circle of the inner drive rotor.
 18. The oil pump of claim 17, wherein the portion is a shallow portion of the outlet port, and the outlet port further has a main portion, and wherein the main portion has an axially extending wall and the shallow portion has a bottom wall extending radially from the axially extending wall.
 19. The oil pump of claim 18, wherein housing defines a back face of the pump cavity, the back face defining inlet and outlet shadow ports that are opposite the inlet and outlet ports, respectively, wherein a portion of the outlet shadow port is radially inboard of the root circle of the inner drive rotor.
 20. The oil pump of claim 19, wherein the portion of the outlet shadow port is a shallow portion, and the outlet shadow port further has a deeper portion that is radially outboard of the root circle of the inner drive rotor. 